In the past, a method for measuring the elevation or the altitude (the height in the vertical direction from 0 meter above sea level) with an air pressure-type altimeter is known. For example, this measurement technique may be used on the ground such as a current location elevation measurement during mountain climbing, or may be used in the air very much away from the ground in the earth's atmosphere such as the altimeter measurement provided in an aircraft.
This air pressure-type altimeter measures on the basis of the following principle.
More specifically, the air existing at any given portion on the earth receives, from the upper side of the air in the vertical direction (the sky), a force corresponding to the weight of the air located in the sky portion due to the gravity (the force of gravity) of the earth. Therefore, the amount of air or the air density is always higher (larger) at the side of the surface of the earth than at the side of the sky, and as a result, the pressure of the air, i.e, the air pressure, is always higher at the side of the surface of the earth than at the side of the sky. If the air is considered to be ideal gas, it is a well-known theory of fluid dynamics that the air pressure exponentially decreases toward the sky (as the altitude becomes higher).
On the other hand, for the measurement of the air pressure with this air pressure-type altimeter, a sensor called an absolute pressure sensor is used in many cases in general.
This absolute pressure sensor is a sensor capable of measuring the air pressure in the earth's atmosphere relative to the vacuum (zero air pressure or zero hectopascal). The change in the air pressure which is commonly referred to as a high atmospheric pressure and a low atmospheric pressure serves as an important index on the basis of a change of the weather, or an important index for predicting the change in the weather from the change in the air pressure in a reverse manner. What measures the air pressure serving as the index is the absolute pressure sensor, and a similar sensor is also used in the air pressure-type altimeter.
However, the air pressure-type altimeter involves the following fundamental problems. That is, the physical amount to be measured is not the altitude itself, and is the air pressure, and therefore, even in a case where the air pressure changes due to a reason other than the altitude, the altitude is deemed to have changed. For this reason, an error occurs between the actual altitude and the current altitude held by the air pressure-type altimeter.
In this case, the factors other than the altitude are, more specifically, the high atmospheric pressure and the low atmospheric pressure explained above, a change in the air pressure due to the flow of the air (wind), or a change in the air pressure that occurs at a border of two or more closed spaces.
For example, in a case where it is necessary to overcome this problem during mountain climbing and correct the altitude, the changes of the altitude and the air pressure in the mountain climbing are often relatively slow, and therefore, it is important to distinguish these changes from the change in the air pressure caused by weather conditions such as the high atmospheric pressure, the low atmospheric pressure, and the like of which changes of the air pressure are likewise relatively slow.
In the actual operation, for example, two types of measures are considered.
The first measure is that, in a case where the elevation is written on a mountain climbing signpost, the mountain climber performs operation to correct the altitude of the altimeter at that location. That is, in this first measure, the mountain climber manually corrects the altitude.
The second measure is that the elevation is found by a three-dimensional measurement of a GPS receiver, and the altitude of the altimeter is corrected at that location. In this second measure, the altitude correction may be automatically executed, or may be manually executed.
On the other hand, in recent years, many buildings called a high building or a super high building are constructed in urban areas in particular, and a person frequently wants to find “the floor in which the person is now located”.
In such situation of the inside of the building, the measurement based on the GPS receiver cannot be performed because the radio wave does not reach the GPS receiver, and instead, it is common to use a barometer (air pressure-type altimeter). Even in a case of movement in the inside of the building, and the air pressure changes due to a factor other than the altitude, there would be an error between the current altitude held in the air pressure-type altimeter and the actual altitude if the altitude is deemed to have changed. For this reason, in the barometer (air pressure-type altimeter), it is desired to provide a method for accurately identifying whether the air pressure has changed due to the change in the altitude or the air pressure has changed due to a factor other than the altitude.
In this case, in a case of movement in the inside of the building, the change in the altitude and the air pressure is often relatively fast (when the change occurs) unlike the case of the mountain climbing explained above. The reason for this is that elevators, escalators, stairs, and the like are generally used to move in the altitude direction of the building, that is, in the vertical direction.
In such case, rather than distinguishing the change in the air pressure caused by the change in the altitude due to the movement from the high atmospheric pressure and the low atmospheric pressure, it is more important to distinguish the change in the altitude and air pressure caused by movement to the upper floor or the lower floor in the inside of the building from the change in the air pressure caused by the flow of the air (wind) or the change in the air pressure that occurs at a border of spaces.
For example, the following technique is known as a technique for distinguishing whether the change in the air pressure is caused by the change of the altitude or the movement in the vertical direction or is caused by the change other than the altitude such as the flow of the air (wind).
PTL 1 discloses a technique in which the altitude and the amount of the change in the altitude are calculated on the basis of the measurement value of a pressure sensor, and when the amount of the change of the altitude is less than a predetermined threshold value, “stationary” is determined. Further, a threshold value larger than the predetermined threshold value is set, and when the amount of the change of the altitude is more than the larger threshold value, “moving” is determined.
PTL 2 discloses a technique in which a movement state such as a stop of elevator movement is determined on the basis of measurement results of the acceleration and the air pressure, the elevator movement stop point is caused to match the layout data stored beforehand.
PTL 3 discloses a technique in which movement in the vertical direction is detected by using a motion sensor other than the pressure sensor, and the altitude is adjusted on the basis of the detection result.
PTL 4 discloses a technique in which the air pressure change speed is calculated from the measurement value of an air pressure sensor, and a probability distribution obtained from a distribution and an average value based on an air pressure change speed stored for each descend and ascend state beforehand and the speed are compared, and the descend and ascend state with the highest probability value is selected.